China's incoming leader Xi Jinping wears an easy grin on his rotund face and often tilts his head to the left in a disarming, almost playful, stance.

But for those who have studied his words to foreign crowds in recent years, the body language may belie his posture on foreign affairs.

"His few public utterances put him closest to the hawkish end of the spectrum," argued columnist Philip Stephens in the Financial Times last month.

Is that true? While Xi's earlier comments, soon after assuming the vice- presidency in 2008, suggest that he was quite the budding hardliner, the aggression has been tempered closer to his succession of President Hu Jintao.

Although he is expected to remain firm on territorial disputes, observers believe he will seek to cool tensions with China's neighbours. "You could say he is in between the doves and the hawks, but leaning slightly to the latter," said analyst Zhou Yongsheng of China Foreign Affairs University.

Such moderation was not evident in his first two years as heir apparent. On his second overseas trip as Vice-President, he was caught on camera, in an unscripted moment with Chinese expatriates, slamming China's critics.

"Some foreigners with full bellies and nothing better to do engage in finger-pointing at us," he said in Mexico in February 2009. "First, China does not export revolution; second, it does not export famine and poverty; and third, it does not mess around with you. So what else is there to say?"

Later that year, Tokyo was reportedly miffed when he insisted on seeing the Emperor on short notice. He got his way.

It got worse. A year later, when Beijing marked the 60th anniversary of China's entry into the Korean War, he called it "a great and just war for safeguarding peace and resisting aggression". North Korea had invaded South Korea but his comments turned it around, angering Seoul.

"There were serious doubts at the time about his competence," said observer June Teufel Dreyer of the University of Miami.

While there have been no recent intemperate remarks in public, the question remains whether he has changed his mind or if he is simply more careful. Being a leader of a big country like China is bound to have some moderating influence, said Professor Dreyer.

Indeed, as Xi grew into the statesman role, his tough talk overseas has eased. This is more in keeping with his background. As a politician, he spent most of his time in the coastal provinces and had regular contact with foreign businesses. He also has family abroad. His older sister is thought to have left China for Canada, while his younger brother spent time in Hong Kong. His only child, Mingze, is studying at Harvard University.

"His wide contacts abroad should give him a better feel of the global scene," said Peking University observer Jia Qingguo.

By the time Xi visited the United States earlier this year, he was on his best behaviour.

And while he had harsh words for Japan in September over the ongoing Diaoyu/Senkaku dispute, it was in keeping with the strong language of his colleagues.

Days later, he turned decidedly dovish when speaking to Asean about the South China Sea. "Having gone through numerous vicissitudes in modern times, we are deeply aware of the importance of development and the preciousness of peace," he said.

Diplomacy expert Li Mingjiang says Xi is hardly a hawk. But he would have no choice but to continue the more assertive stance which Beijing has adopted since 2009 on territorial disputes.

"Nationalism is on the rise in China... it will be very difficult for Xi and his colleagues to appear to make any concessions to other countries," said the analyst from the S. Rajaratnam School of International Studies in Singapore. "Doing so will further aggravate the sense of frustration and victimisation among the Chinese public and as a result weaken the legitimacy of the ruling elite."

So he must appear tough. But as Prof Dreyer pointed out: "The real question is how aggressively he will do so."